1. Field of the Invention
The present invention relates to woven, endless tire reinforcement belts.
In recent years, endless woven tire reinforcement belts have been shown to provide a number of advantages over breaker belts of more conventional construction. These endless belts are woven from coated continuous reinforcement material by laying it in an ordered zig-zag pattern on the surface of a forming drum of predetermined diameter.
The present invention relates to further improvements in woven endless tire reinforcing belts and a method for producing same, the improvements concerning changing the zig-zag pattern of the endless belt weave.
2. Discussion of the Prior Art
Endless reinforcements for belted tires are known in the art. U.S. Pat. No. 3,589,426 to Varner shows an endless reinforcement for a pneumatic tire comprising continuous cord forming a generally zig-zag pattern and being positioned across the width of the reinforcement from one side to the other at an angle to the edges of the reinforcement with reversals at the edges. The relationship of the various parameters of the reinforcement is as follows: ##EQU1## wherein C is the circumference of the reinforcement, A is the smaller angle between the cord and the edge of the reinforcement, W is the width of the reinforcement measured perpendicular to the edges, EPI is the number of cords per inch measured perpendicular to the cord lengths, P is an integer and equal to one plus the total number of interleaving lines parallel to and intermediate the edges of the reinforcement, M and D are two integers having no common factor and which render (P.multidot.M+1/D) an integer with D being less than P, and D and P have no common factor, and GR is the number of repeating cycles of the cord from one edge and back to the same edge for each circumference of the reinforcement.
Varner '426 also provides that the edges of the reinforcement of the invention may be distorted by providing cord reversals at points staggered with respect to other reversal points, such that the point of reversal for a given length of cord may be closer to or farther away from the center as desired to provide a reinforcement with edges somewhat thinner than the main body of the reinforcement (column 3, lines 61-67).
U.S. Pat. No. 3,729,365 to Greene discloses a reinforcing strip 11 disposed in a zig-zag repeating pattern with succeeding lengths of the strip being displaced from each other. The reversal points or folds 12 are at the edges of the reinforcement. The Green patent also states at column 3, lines 33-42, that it may be desirable to provide a change in the angle of the strip across the width of the reinforcement, for example, by making the angle in portions of the strip adjacent the edges greater or less than the angle in the center portion. Greene does not disclose what the angles or change in angles should be, however.
U.S. Pat. No. 3,746,590 to Barley et al. shows a pneumatic tire having a belt wound from a tape wherein the successive superposed windings forming the edges of belt 14 is said to provide a build-up or greater thickness of cords for the shoulder or edge portion of the tread.
It is a disadvantage of the prior art woven belts that the cord reinforcements tend to accumulate toward the edges of the belt where the reversals occur, thereby making the belt thicker and therefore stiffer adjacent the edges than toward the center. This structure can cause uneven tread wear across the tire, with possibly greater center wear taking place than is desirable.